The present invention relates generally to a dynamic behavior control apparatus for an automotive vehicle, and more specifically, to a method and apparatus for determining whether a wheel of an automotive vehicle has lifted from the pavement.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at various wheels of the vehicle. By regulating the amount of braking at each corner of the vehicle, the desired direction of the vehicle may be maintained.
Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristics of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
Vehicle rollover and tilt control (or body roll) are distinguishable dynamic characteristics. Tilt control maintains the body on a plane or nearly on a plane parallel to the road surface. Rollover control is used to maintain the vehicle wheels on the road surface.
Such systems typically use position sensors to measure the relative distance between the vehicle body and the vehicle suspension. One drawback to such systems is that the distance from the body to the road must be inferred.
It would therefore be desirable to provide a rollover detection system having reduced costs and increased reliability in predicting the occurrence of a rollover.
It is therefore one object of the invention to provide a rollover detection system that may be used in conjunction with the dynamic stability control system of the vehicle to determine rollover.
In one aspect of the invention, a wheel lift identification system for an automotive vehicle includes a speed sensor coupled to the vehicle producing a wheel speed signal. A torque control system is coupled to the wheel for changing the torque at the wheel. A controller is coupled to the torque control system and the speed sensor. The controller determines lift by changing the torque of the wheel, measuring the change in wheel speed since the torque was changed, and indicating a wheel lift if the change in the wheel speed is greater than a predetermined value.
In a further aspect of the invention, a method for determining wheel lift of a vehicle comprises the steps of:
changing the torque of a wheel;
measuring the change in wheel speed since the step of changing torque; and,
indicating wheel lift if the change in wheel speed is greater than a predetermined value.
In a further aspect of the invention, the changing of the torque of the wheel may be performed by increasing the brake pressure for that wheel. When the wheel speed has significant deceleration, a wheel flag is set. When the brake pressure is released and the wheel speed changes greater than a reacceleration threshold, then wheel contact is assumed. If the wheel speed does not increase over the reacceleration threshold within a predetermined time, then wheel lift status is confirmed. As an alternative, driveline torque may be used.
One advantage of the invention is that in vehicles employing a dynamic stability control system, additional sensors may not be required.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.